1. Field of the Invention
The present invention relates to a heating device for use in heating a semiconductor wafer and the like.
2. Description of the Related Art
In a manufacturing process of a semiconductor device, a heating treatment is implemented in order to form an oxidation film and the like on a wafer by using a semiconductor manufacturing apparatus. As an example of a heating device for implementing the heating treatment in the semiconductor manufacturing apparatus, there is a ceramic heater including a disc-like ceramic base having a heating surface on which a heating object is set, in which a linear resistance heating body is embedded in the ceramic base. One or plural lines of the linear resistance heating bodies of the ceramic heater are embedded in a wiring pattern parallel to the heating surface of the ceramic base. A voltage is applied to both ends of the lines, and the heating surface is thereby made to generate heat.
Moreover, in the ceramic heater, there is one in which a disc-like high frequency electrode capable of applying a high frequency is embedded in an inside of the ceramic base in the vicinity of the heating surface. The high frequency electrode constructs a pair of plasma electrodes, for example, together with an opposite electrode disposed adjacent to the heating surface oppositely thereto in a space above the ceramic base. Electric power is supplied to the high frequency electrode and the opposite electrode, thus making it possible to generate high frequency plasma in a space in the vicinity of the heating object set on the heating surface. Moreover, the high frequency electrode can also be used for applying a bias voltage to the heating object.
As a material used for the ceramic base of the ceramic heater, a material having sufficiently high electrical resistivity or having insulating property against such a resistance heating element at an operation temperature at which the treatment object is heated. The reason is as follows. Specifically, when the material of the ceramic body has conductivity, a part of a current supplied in order to heat the resistance heating body flows through the ceramic base. Then, a region other than the resistance heating body generates heat, or a desired current does not flow through the resistance heating body. As a result, the resistance heating body is inhibited from performing uniform heating all over the heating surface, that is, uniform heating performance of the ceramic body is significantly damaged.
Therefore, as the material of the base of the ceramic heater, aluminum nitride (AlN) is frequently used. Aluminum nitride is good in heat resistance and corrosion resistance, has high thermal conductivity and high resistivity. In terms of these characteristics, aluminum nitride is suitable for the base of the ceramic heater.
With regard to a sintered body using aluminum nitride as described above, there is an aluminum nitride sintered body mixed with carbon fiber in order to obtain volume resistivity suitable for use as an electrostatic chuck (Japanese Patent Laid-Open Publication No. 2005-41765).
Moreover, with regard to a susceptor having low volume resistivity, there is a ceramic-made susceptor having a stacked two-layer structure of a surface layer having a mounting surface on which the treatment object is mounted and of a support layer supporting the surface layer, in which the surface layer entirely has lower volume resistivity than the support layer (Japanese Patent Laid-Open Publication No. 2002-134590).
In the ceramic heater, and in particular, in a ceramic heater in which the high frequency electrode is embedded in the ceramic base, when the plasma is generated at the time of heating, a part of plasma charges remains and is accumulated in the heating surface of the ceramic heater. Thus, when the heating object such as the wafer is detached from the heating surface, the accumulated charges may be discharged to the heating object. Such discharge is called arcing, which brings a damage of the wafer and a generation of particles.
Moreover, by the fact that a part of the plasma charges remains on the heating surface of the ceramic heater, the wafer or the like set on the heating surface of the ceramic heater is sucked to the surface of the heater by electrostatic force due to the remaining charges, causing difficulty in detaching the wafer or the like.
Furthermore, a ring-like member may be mounted on a periphery of the wafer set on the heating surface in order to prevent unintended etching on the ceramic base at the time of the plasma generation. The charges caused by the plasma may be accumulated in the ring-like member. Then, such arcing in which the charges are discharged to the other members or the heating object occurs at the time when certain amount of the charges are accumulated in the ring-like member, leading to a breakage of the heating object and the like and the generation of the particles.
In this connection, it is an object of the present invention to provide a heating device that suppresses the charges from remaining on the ceramic base and the ring-like member, thus making it possible to effectively prevent an occurrence of the arcing.